Ken - 1972 and earlier seafaris won't have a HIN number stamped on the transom. They had a sticker right under the steering wheel with 4 or 5 digit Hull ID (model and Hull number). 4 hollow stringers is 1972 or earlier . . . 1970, 1971 or 1972.
In 1975 or 1976 they changed a few things like the windshield design. The later windshield design is a split window (see picture). The earlier one doesn't have the split window.
There were no seafari's built after 1979.
http://www.classicseacraft.com/broch...production.pdf